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RE: IBC Fire Walls and Seismic Code

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There are several ways to design firewalls:
 
Cantlivered
Tied
Double
Weak Link
 
With steel structures, you must provide enough distance between structures for the steel to expand without damaging the firewall(s). This distance varies 2 1/2" and 7 1/2".
 
I would think that the double firewall or tied firewall would be the common way to design in seismic areas.
 
The IBC gives little guidance to the engineer on how to design these firewalls. The best references are NFPA 221, FM, NCMA and Commentary M of the Canadian Code.
 
Jim K.
-----Original Message-----
From: Paul Feather [mailto:pfeather(--nospam--at)SE-Solutions.net]
Sent: Wednesday, April 26, 2006 2:00 PM
To: SEAOC List
Subject: IBC Fire Walls and Seismic Code

Under the IBC, the area separation walls from the UBC are gone, and the corresponding wall is a Fire Wall.
 
The primary difference is the ability of one side of the structure to collapse, without taking down the wall.  The commentary clearly shows the diaphragm sheathing as discontinuous at the Fire Wall in Type V construction.
 
Question, how does this square with the seismic code provisions where all parts of the structure are to be interconnected, or a separation joint is to be provided?  Are we now supposed to provide 4 to 8 inch seismic joints at all area separation walls, essentially breaking the building into multiple buildings? 
 
Under the UBC Area Separation Walls it was permissible to have the sheathing extend through at the floor diaphragms, and the only problem was maintaining the rating through the assembly.
 
What are other people doing about this condition?